Method of using thick first spacers to improve salicide resistance on polysilicon gates

ABSTRACT

A method and device for improved salicide resistance in polysilicon gates under 0.20 μm. The several embodiments of the invention provide for formation of gate electrode structures with recessed and partially recessed spacers. One embodiment, provides a gate electrode structure with recessed thick inner spacers and thick outer spacers. Another embodiment provides a gate electrode structure with recessed thin inner spacers and recessed thick outer spacers. Another embodiment provides a gate electrode structure with thin inner spacers and partially recessed outer spacers. Another embodiment provides a gate electrode structure with two spacer stacks. The outermost spacer stack with recessed thin inner spacers and recessed thick outer spacers. The inner spacer stack with thin inner spacers and thin outer spacers. Another embodiment provides a gate electrode structure with two spacer stacks. The outermost spacer stack with recessed thin inner spacers and recessed thick outer spacers. The inner spacer stack with recessed thin inner spacers and recessed thin outer spacers.

FIELD OF THE INVENTION

The present invention relates to the field of semiconductor devices.More particularly, the present invention relates to a method and devicefor improved resistance on gate electrodes. Specifically, the presentinvention relates to a method and device for improved salicideresistance on polysilicon gates.

BACKGROUND OF THE INVENTION

Transistors are commonly used in semiconductor circuitry to controlcurrent flow. For example, a transistor can be used as a switchingmechanism to allow the flow of current between a source and a drainregion in a circuit when a certain threshold voltage is met. Transistorsgenerally include a gate electrode that allows or prevents the flow ofcurrent in the transistor based on applied voltage.

FIG. 1a shows a cross-sectional view of a conventional gate electrode100 formed on a substrate 110, the underlying structure of which is notshown. It should be noted that the figures are merely illustrative andhave been simplified for clarity purposes. A thin insulative layer 120is formed on the substrate 110 to act as a barrier between the substrate110 and the conductive portions of the gate electrode 100. An example ofan insulative layer 120 can be an oxide layer, such as silicon dioxide(SiO₂). Formed on the insulative layer 120 is a gate layer 130. Anexample of a gate layer 130 can be a polysilicon layer. Formed on thegate layer 130 is a conductive layer 160. An example of a conductivelayer 160 can be a polycide layer, such as titanium salicide (TiSi₂).When a threshold voltage is applied to the gate layer 130 by theconductive layer 160, current will flow through the gate layer 130.Often insulative spacers 140 and 150 are formed to each side of the gatelayer 130 to prevent transfer of current between the gate layer 130 andsurrounding structures in the semiconductor.

In semiconductor circuit design, frequently, gate electrodes aredesigned in long continuous lines on the semiconductor substrate toefficiently provide current to several transistors in a circuit.Currently, improved semiconductor transistor performance is beingachieved through device scaling in which the gate layer widths are beingreduced from 0.20 μm to 0.15 μm and below (sub-0.15 μm). As the gatelayer width dimensions decrease, so do the conductive layer line widthsformed above them.

When the gate layer widths decrease below 0.20 μm, current processtechniques produce conductive lines with sharply increasing resistance.This is detrimental to the efficiency of the semiconductor, as higherresistance decreases the speed of the semiconductor circuitry.Additionally, process yields drop due to defective conductive lineformation reducing manufacturing output. These problems have beenparticularly noted in current fabrication processes where titaniumsalicide (TiSi₂) is formed as the conductive layer in a polysilicongate.

FIG. 1b illustrates a cross-sectional view of a conventional gateelectrode 100 formed on a substrate 110, the underlying structure ofwhich is not shown. An example of a gate electrode 100 can be apolysilicon gate electrode. Formed on the substrate 110 is an insulativelayer 120. An example of an insulative layer 120 can be an oxide. Formedon the insulative layer 120 is a conductive gate layer 130. An exampleof a gate layer 130 is a polysilicon layer. Formed on the gate layer 130is a conductive layer 160. An example of a conductive layer 160 can be apolycide, such as titanium salicide. Insulative spacers 140 and 150 areformed adjacent to the gate layer 130 and conductive layer 160 toprevent current flow between the gate layer 100 and surroundingstructures.

During formation of the conductive layer 160, components from underlyinggate layer 130 often out diffuse into a reactant layer that is used toform the conductive layer 160. For example, silicon components of anunderlying gate layer 130 may out diffuse into the conductive layer 160.This out diffusion results in a conductive layer 160 wider than the gatelayer 130. When the gate layer 100 width is decreased below 0.20 μm, theconductive layer 160 becomes stressed by its enclosure between the sidewalls of the spacers 140. This results in increased resistance in theconductive layer 160. Increased resistance in the conductive layerdirectly impacts the quality of the semiconductor circuit. The circuitbecomes inefficient and circuit failure or device failure may occur.

Another result of decreasing the gate line widths below 0.20 μm is adecrease in process yields. This is due to non-formation of theconductive layer. This is attributed to the reduced reaction area, ornucleation sites, available at such small dimensions. The reduceddimensions of the gate layer reduces nucleation sites on which theconductive layer can form during processing. Using current processtechniques, if sufficient nucleation sites are not provided, theconductive layer often won't form. This directly impacts thesemiconductor manufacturer by reducing output.

Based on the above described problems, it would be desirable to have amethod and/or device which will improve the polycide resistance inpolysilicon gate widths below 0.20 μm.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a method and a device which improvespolycide resistance in gate electrode widths below 0.20 μm. Theinvention provides several embodiments one embodiment of which isdescribed below.

In one embodiment of the present invention there is provided a gateelectrode comprising a thin insulative layer. A gate layer is formed onthe thin insulative layer. A conductive layer is formed on the gatelayer. Thick first spacers are formed adjacent to opposite sides of thegate layer. Thick second spacers are formed adjacent to the thick firstspacers. The thick first spacers are recessed to create an open spacebetween the gate layer and thick second spacers.

BRIEF DISCUSSION OF THE SEVERAL VIEWS OF THE DRAWINGS

For fuller understanding of the present invention, reference is made tothe accompanying drawings in the following detailed description of theinvention. In the drawings:

FIG. 1(a) is a cross-sectional illustration of a conventional gateelectrode in the prior art depicting a non-stressed conductive layer.

FIG. 1(b) is a cross-sectional illustration of a conventional gateelectrode in the prior art depicting a stressed conductive layer.

FIGS. 2(a)-(h) are cross-sectional illustrations of the formation of agate electrode with a conductive layer and recessed thick inner spacersand non-recessed thick outer spacers.

FIGS. 3(a)-(i) are cross-sectional illustrations of the formation of agate electrode with a conductive layer and recessed thin inner spacersand recessed thick outer spacers.

FIGS. 4(a)-(i) are cross-sectional illustrations of the formation of agate electrode with a conductive layer and non-recessed thin innerspacers and partially recessed outer spacers.

FIGS. 5(a)-(m) are cross-sectional illustrations of the formation of agate electrode with a conductive layer and two spacer stacks. Theoutermost spacer stack having recessed thin inner spacers and recessedthick outer spacers. The inner spacer stack having non-recessed thininner spacers and non-recessed thin outer spacers.

FIGS. 6(a)-(p) are cross-sectional illustrations of the formation of agate electrode with a conductive layer and two spacer stacks. Theoutermost spacer stack having recessed thin inner spacers and recessedthick outer spacers. The inner spacer stack having recessed thin innerspacers and recessed thin outer spacers.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a method and a device to improve polycideresistance on gate electrodes less than 0.20 μm in width. In thefollowing description of the several embodiments of the invention,numerous details are set forth in order to provide a thoroughunderstanding of the present invention. It will be appreciated by onehaving ordinary skill in the art that the present invention may bepracticed without such specific details. In other instances, well knownstructures and techniques have not been described in detail in order toavoid obscuring the subject matter of the present invention. It will beunderstood by those having ordinary skill in the art that the structuresof the present invention may be formed by various techniques.

Referring now to the drawings, one embodiment of the present inventionis shown in FIGS. 2a-h. FIG. 2a illustrates a gate layer 220 formed on athin insulative layer 210 on a substrate 200. In one embodiment, thegate layer 220 can be a polysilicon. In one embodiment, the gate layer220 is less than 0.20 μm in width. These structures are formed usingconventional deposition and etching techniques well-known in the art.

In FIG. 2b, a thick first spacer layer 230 is deposited or grown on thegate layer 220 and substrate 200. In one embodiment, the thick firstspacer layer 230 can be an oxide. In one embodiment, the thick firstspacer layer 230 can be deposited or grown to a thickness in the rangeof approximately 200-600 Å, for example, 300 Å. It should be noted thatthe thick first spacer layer 230 can be deposited or grown usingdeposition techniques that are well known in the art and are notdescribed in detail herein.

In FIG. 2c, a thick second spacer layer 240 is deposited or grown on thethick first spacer layer 230. In one embodiment, the thick second spacerlayer 240 can be a nitride. In one embodiment, the thick second spacerlayer 240 can be deposited or grown to a thickness in the range ofapproximately 300-2000 Å, for example, 800 Å. It should be noted thatthe thick second spacer layer 240 can be deposited or grown usingdeposition techniques that are well known in the art and are notdescribed in detail herein.

The thick second spacer layer 240 is etched to form the spacer structureillustrated in FIG. 2d. In one embodiment, this etch is an anisotropic(directional) etch which will remove nitride, but not oxide. Examples ofanisotropic etches are a dry etch or a plasma etch.

The thick first spacer layer 230 is recessed by etching to form thespacer structure illustrated in FIG. 2e. The recessing creates an openspace between the thick second spacer layer 240 and the gate layer 220.In one embodiment, the thick first spacer layer 230 is etchedapproximately 60 nm deeper than the surface of the gate layer 220. Inone embodiment, the etching forms a space approximately 200-600 Å, forexample, 300 Å, between the thick second spacer layer 240 and the gatelayer 220. In one embodiment this etch is an isotropic(multidirectional) etch which will remove oxide, but not nitride.Examples of isotropic etches are dry or wet etches. It should be notedthat the side walls of the gate layer 220 are now exposed creating alarger contact (reaction) surface area.

In FIG. 2f, a reactant layer 250 is deposited, for example by sputter,electron beam evaporation, chemical vapor, or plasma deposition. In oneembodiment, the reactant layer 250 can be a metal, such as titanium.

The reactant layer 250 and the gate layer 220 are then annealed to forma conductive layer 260 as shown in FIG. 2g. In one embodiment, theformed conductive layer 260 can be a polycide, such as titaniumsalicide. A polycide may also be called a polysilicide. It should benoted that silicides can be self-aligning or non-self-aligning, and ifthe silicide is self-aligning, it may be called a salicide. It is to beunderstood by one of ordinary skill in the art that polycides, otherthan self-aligning silicides, may also be formed. In one embodiment, theanneal may be performed using a rapid thermal annealing process in anitrogen ambient. In one embodiment, additional anneals can be performedto decrease the resistance of the conductive layer 260. It is to benoted that the conductive layer 260 can now extend beyond the edges ofthe gate layer 220 and is not constrained and stressed by the thickfirst spacer layer 230.

The unreacted portion of reactant layer 250 is etched away leaving theconductive layer 260 as illustrated in FIG. 2h. In one embodiment, thisetch is an isotropic etch which will remove unreacted titanium, but nottitanium salicide.

Another embodiment of the present invention is illustrated in FIGS.3a-i. FIG. 3a illustrates a gate layer 320 formed on a thin insulativelayer 310 on a substrate 300. In one embodiment, the gate layer 320 canbe a polysilicon. In one embodiment, the gate layer 320 is less than0.20 μm in width. These structures are formed using conventionaldeposition and etching techniques well-known in the art.

In FIG. 3b, a thin first spacer layer 330 is deposited or grown on thegate layer 320 and substrate 300. In one embodiment, the thin firstspacer layer 330 can be an oxide. In one embodiment, the thin firstspacer layer 330 is deposited or grown to a thickness in the range ofapproximately 50-300 Å, for example, 100 Å. It should be noted that thethin first spacer layer 330 can be deposited or grown using depositiontechniques that are well known in the art and are not described indetail herein.

In FIG. 3c, a thick second spacer layer 340 is deposited or grown on thethin first spacer layer 330. In one embodiment, the thick second spacerlayer 340 can be a nitride. In one embodiment, the thick second spacerlayer 340 is deposited or grown to a thickness in the range ofapproximately 300-2000 Å, for example, 800 Å. It should be noted thatthe thick second spacer layer 340 can be deposited or grown usingdeposition techniques that are well known in the art and are notdescribed in detail herein.

The thick second spacer layer 340 is etched a first time to form thestructure illustrated in FIG. 3d. In one embodiment, this etch is ananisotropic (directional) etch which will remove nitride, but not oxide.Examples of anisotropic etches are a dry etch or a plasma etch.

The thick second spacer layer 340 is then recessed by etching a secondtime to form the spacer structure illustrated in FIG. 3e. In oneembodiment, the thick second spacer layer 340 is etched approximately 60nm deeper than the surface level of the gate layer 320. In oneembodiment, this etch is an isotropic (multidirectional) etch which willremove nitride, but not oxide. Examples of isotropic etches are a wet ordry etch.

The thin first spacer layer 330 is then recessed by etching to form thespacer structure illustrated in FIG. 3f. In one embodiment, this etch isan isotropic (multidirectional) etch which will remove oxide, but notnitride. Examples of isotropic etches are a dry, wet or chemical bathetch. It should further be noted that the side walls of the gate layer320 are now exposed creating a larger contact (reaction) surface area

In FIG. 3g, a reactant layer 350 is deposited, for example, by sputter,electron beam evaporation, chemical vapor, or plasma deposition. In oneembodiment, the reactant layer 350 can be a metal, such as titanium.

The reactant layer 350 and the gate layer 320 are then annealed to forma conductive layer 360 as shown in FIG. 3h. In one embodiment, theformed conductive layer 360 can be a polycide, such as titaniumsalicide. A polycide may also be called a polysilicide. It should benoted that silicides can be self-aligning or non-self-aligning, and ifthe silicide is self-aligning, it may be called a salicide. It is to beunderstood by one of ordinary skill in the art that polycides, otherthan self-aligning silicides, may also be formed. In one embodiment, theanneal may be performed using a rapid thermal annealing process in anitrogen ambient. In one embodiment, additional anneals can be performedto decrease the resistance of the conductive layer 360. It is to benoted that the conductive layer 360 can now extend beyond the edges ofthe gate layer 320 and is not constrained and stressed.

The unreacted portion of reactant layer 350 is etched away leaving theconductive layer 360 as illustrated in FIG. 3i. In one embodiment, thisetch is an isotropic etch which will remove unreacted titanium, but nottitanium salicide.

Another embodiment of the present invention is illustrated in FIGS.4a-i. FIG. 4a illustrates a gate layer 420 formed on a thin insulativelayer 410 on a silicon substrate 400. In one embodiment, the gate layer420 can be polysilicon. In one embodiment, the gate layer 420 is lessthan 0.20 μm in width. These structures are formed using conventionaldeposition and etching techniques well-known in the art.

In FIG. 4b, a thin first spacer layer 430 is deposited or grown on thegate layer 420 and substrate 400. In one embodiment, the thin firstspacer layer 430 can be an oxide. In one embodiment, the thin firstspacer layer 430 is deposited or grown to a thickness in the range ofapproximately 50-300 Å, for example, 100 Å. It should be noted that thethin first spacer layer 430 can be deposited or grown using depositiontechniques that are well known in the art and are not described indetail herein.

In FIG. 4c, a thick second spacer layer 440 is deposited or grown on thethin first spacer layer 430. In one embodiment, the thick second spacerlayer 440 can be a nitride. In one embodiment, the thick second spacerlayer 440 can be deposited or grown to a thickness in the range ofapproximately 300-2000 Å, for example, 800 Å. It should be noted thatthe thick second spacer layer 440 can be deposited or grown usingdeposition techniques that are well known in the art and are notdescribed in detail herein.

The thick second spacer layer 440 is etched a first time to form thestructure illustrated in FIG. 4d. In one embodiment, this etch is ananisotropic (directional) etch which will remove nitride, but not oxide.Examples of anisotropic etches are a dry etch or a plasma etch.

The thick second spacer layer 440 is then partially recessed by etchinga second time to form the spacer structure illustrated in FIG. 4e. Inone embodiment, the partial recess creates a thin second spacer wall 470adjacent to the thin first spacer layer 430. In one embodiment, the thinsecond spacer wall 470 can be in the range of approximately 50-200 Å,for example, 100 Å, in width and can extend approximately 60 nm deeperthan the surface level of the gate layer 420. In one embodiment, thisetch is an anisotropic (directional) etch which will remove nitride, butnot oxide. Examples of anisotropic etches are a dry etch or a plasmaetch.

Following the partial recessing of the thick second spacer layer 440,the thin first spacer layer 430 is etched to form the spacer structureillustrated in FIG. 4f. In one embodiment, this etch is an isotropic(multidirectional) etch which will remove oxide, but not nitride.Examples of isotropic etches are a dry, wet or chemical bath etch.

In FIG. 4g, a reactant layer 450 is deposited, for example, by sputter,electron beam evaporation, chemical vapor, or plasma deposition. In oneembodiment, the reactant layer 450 can be a metal, such as titanium.

The reactant layer 450 and the gate layer 420 are then annealed to forma conductive layer 460 as shown in FIG. 4h. In one embodiment, theconductive layer 460 can be a polycide, such as titanium salicide. Apolycide may also be called a polysilicide. It should be noted thatsilicides can be self-aligning or non-self-aligning, and if the silicideis self-aligning, it may be called a salicide. It is to be understood byone of ordinary skill in the art that polycides, other thanself-aligning silicides, may also be formed. In one embodiment, theanneal may be performed using a rapid thermal annealing process in anitrogen ambient. In one embodiment, additional anneals can be performedto decrease the resistance of the conductive layer 460. It is to benoted that the conductive layer 460 can now extend beyond the edges ofthe gate layer 420 due to flexibility in the thin spacer walls formedfrom the thin first spacer layer 430 and the thin second spacer walls470.

The unreacted portion of reactant layer 450 is etched away leaving theconductive layer 460 as illustrated in FIG. 4i. In one embodiment, thisetch is an isotropic etch which will remove unreacted titanium, but nottitanium salicide.

Another embodiment of the present invention is illustrated in FIGS.5a-m. FIG. 5a illustrates a gate layer 520 formed on a thin insulativelayer 510 on a substrate 500. In one embodiment, the gate layer 520 canbe polysilicon. In one embodiment, the polysilicon gate layer 520 isless than 0.20 μm in width. These structures are formed usingconventional deposition and etching techniques well-known in the art.

In FIG. 5b, a thin first spacer layer 530 is deposited or grown on thegate layer 520 and substrate 500. In one embodiment, the thin firstspacer layer 530 can be an oxide. In one embodiment, the thin firstspacer layer 530 is deposited or grown to a thickness in the range ofapproximately 50-150 Å, for example, 50 Å. It should be noted that thethin first spacer layer 530 can be deposited or grown using depositiontechniques that are well known in the art and are not described indetail herein.

In FIG. 5c, a thin second spacer layer 540 is deposited or grown on thethin first spacer layer 530. In one embodiment, the thin second spacerlayer 540 can be a nitride. In one embodiment, the thin second spacerlayer 540 can be deposited or grown to a thickness in the range ofapproximately 50-150 Å, for example, 50 Å. It should be noted that thethin second spacer layer 540 can be deposited or grown using depositiontechniques that are well known in the art and are not described indetail herein.

The thin second spacer layer 540 is etched a first time to form thestructure illustrated in FIG. 5d. In one embodiment, this etch is ananisotropic (directional) etch which will remove nitride, but not oxide.Examples of anisotropic etches are a dry etch or a plasma etch.

Following the etch of the thin second spacer layer 540, the thin firstspacer layer 530 is etched to form the structure illustrated in FIG. 5e.In one embodiment, this etch is an isotropic (multidirectional) whichwill remove oxide, but not nitride. Examples of isotropic etches are dryor wet etches. It should be further noted that at this point in aprocess flow, implants of dopants can be added to the structure toenhance circuit performance.

In FIG. 5f, a thin third spacer layer 550 is deposited or grown. In oneembodiment, the thin third spacer layer 550 can be an oxide. In oneembodiment, the thin third spacer layer 550 is deposited or grown to athickness in the range of approximately 50-300 Å, for example, 100 Å. Itshould be noted that the thin third spacer layer 550 can be deposited orgrown using deposition techniques that are well known in the art and arenot described in detail herein.

In FIG. 5g, a thick fourth spacer layer 560 is deposited or grown on thethin third spacer layer 550. In one embodiment, the thick fourth spacerlayer 560 can be a nitride. In one embodiment, the thick fourth spacerlayer 560 is deposited or grown to a thickness in the range ofapproximately 300-2000 Å, for example, 800 Å. It should be noted thatthe thick fourth spacer layer 560 can be deposited or grown usingdeposition techniques that are well known in the art and are notdescribed in detail herein.

The thick fourth spacer layer 560 is etched a first time to form thestructure illustrated in FIG. 5h. In one embodiment, this etch is ananisotropic (directional) etch which will remove nitride, but not oxide.Examples of anisotropic etches are a dry etch or a plasma etch.

The thick fourth spacer layer 560 is then recessed by etching a secondtime to form the spacer structure illustrated in FIG. 5i. In oneembodiment, the thick fourth spacer layer 560 is etched approximately 60nm deeper than the surface level of the gate layer 520. In oneembodiment, this etch is an isotropic (multidirectional) etch which willremove nitride, but not oxide. Examples of isotropic etches are wet ordry etches.

The thin third spacer layer 550 is then recessed by etching to form thespacer structure illustrated in FIG. 5j. In one embodiment, this etch isan isotropic (multidirectional) etch which will remove oxide, but notnitride. Examples of isotropic etches are a dry, wet or chemical bathetch.

In FIG. 5k, a reactant layer 570 is deposited, for example, by sputter,electron beam evaporation, chemical vapor, or plasma deposition. In oneembodiment, the reactant layer 570 can be a metal such as titanium.

The reactant layer 570 and the gate layer 520 are then annealed to forma conductive layer 580 as shown in FIG. 5l. In one embodiment, theconductive layer 580 can be a polycide, such as titanium salicide. Apolycide may also be called a polysilicide. It should be noted thatsilicides can be self-aligning or non-self-aligning, and if the silicideis self-aligning, it may be called a salicide. It is to be understood byone of ordinary skill in the art that polycides, other thanself-aligning silicides, may also be formed. In one embodiment, theanneal may be performed using a rapid thermal annealing process in anitrogen ambient. In one embodiment, additional anneals can be performedto decrease the resistance of the conductive layer 580. It is to benoted that the conductive layer 580 can now extend beyond the edges ofthe gate layer 520 due to flexibility in the thin spacer walls formedfrom the thin first spacer layer 530 and the thin second spacer layer540.

The unreacted reactant layer 570 is etched away leaving the conductivelayer 580 as illustrated in FIG. 5m. In one embodiment, this etch is anisotropic etch which will remove unreacted titanium, but not titaniumsalicide.

Another embodiment of the present invention is illustrated in FIGS.6a-p. FIG. 6a illustrates a gate layer 620 formed on a thin insulativelayer 610 on a substrate 600. In one embodiment, the gate layer 620 canbe polysilicon. In one embodiment, the gate layer 620 is less than 0.20μm in width. These structures are formed using conventional depositionand etching techniques well-known in the art.

In FIG. 6b, a thin first spacer layer 630 is deposited or grown on thegate layer 620 and substrate 600. In one embodiment, the thin firstspacer layer 630 can be an oxide. In one embodiment, the thin firstspacer layer 630 is deposited or grown to a thickness in the range ofapproximately 50-150 Å, for example, 50 Å. It should be noted that thethin first spacer layer 630 can be deposited or grown using depositiontechniques that are well known in the art and are not described indetail herein.

In FIG. 6c, a thin second spacer layer 640 is deposited or grown on thethin first spacer layer 630. In one embodiment, the thin second spacerlayer 640 can be a nitride. In one embodiment, the thin second spacerlayer 640 can be deposited or grown to a thickness in the range ofapproximately 50-150 Å, for example, 50 Å. It should be noted that thethin second spacer layer 640 can be deposited or grown using depositiontechniques that are well known in the art and are not described indetail herein.

The thin second spacer layer 640 is etched a first time to form thestructure illustrated in FIG. 6d. In one embodiment, this etch is ananisotropic (directional) etch which will remove nitride, but not oxide.Examples of anisotropic etches are a dry etch or a plasma etch.

Following the etch of the thin second spacer layer 640, the thin firstspacer layer 630 is etched to form the structure illustrated in FIG. 6e.In one embodiment, this etch is an isotropic (multidirectional) whichwill attack oxide, but not nitride. Examples of isotropic etches are adry, wet or chemical bath etch. It should be further noted that at thispoint in a process flow, implants of dopants can be added to thestructure to enhance circuit performance.

In FIG. 6f, a thin third spacer layer 650 is deposited or grown. In oneembodiment, the thin third spacer layer 650 can be an oxide. In oneembodiment, the thin third spacer layer 650 is deposited or grown to athickness in the range of approximately 50-300 Å, for example 100 Å. Itshould be noted that the thin third spacer layer 650 can be deposited orgrown using deposition techniques that are well known in the art and arenot described in detail herein.

In FIG. 6g, a thick fourth spacer layer 660 is deposited or grown on thethin third spacer layer 650. In one embodiment, the thick fourth spacerlayer 660 can be a nitride. In one embodiment, the thick fourth spacerlayer 660 is deposited or grown to a thickness in the range ofapproximately 300-2000 Å, for example, 800 Å. It should be noted thatthe thick fourth spacer layer 660 can be deposited or grown usingdeposition techniques that are well known in the art and are notdescribed in detail herein.

The thick fourth spacer layer 660 is etched a first time to form thestructure illustrated in FIG. 6h. In one embodiment, this etch is ananisotropic (directional) etch which will remove nitride, but not oxide.Examples of anisotropic etches are a dry etch or a plasma etch.

The thick fourth spacer layer 660 is then recessed by etching a secondtime to form the spacer structure illustrated in FIG. 6i. In oneembodiment, the thick fourth spacer layer 660 is etched approximately 60nm deeper than the surface level of the gate layer 620. In oneembodiment, this etch is an isotropic (multidirectional) etch which willremove nitride, but not oxide. Examples of isotropic etches are a wet ordry etch.

The thin third spacer layer 650 is then recessed by etching to form thespacer structure illustrated in FIG. 6j. In one embodiment, this etch isan isotropic (multidirectional) etch which will remove oxide, but notnitride. Examples of isotropic etches are dry or wet etches.

At this point, further etches are still to be performed, however, thesubstrate 600 is left exposed. Thus, if a following etch chemistry isutilized which can remove the substrate 600, the substrate 600 will needto be protected. Thus, a protective layer, for example, an oxide layer,can be provided. The provision of a protective layer is describedtogether with the figures that follow. Alternatively, if a followingetch chemistry does not remove the substrate 600, then the process cancontinue without the necessity of providing and removing a protectivelayer.

In FIG. 6k, a thin protective layer 670 is deposited or grown on thesubstrate 600. In one embodiment, the thin protective layer 670 can beoxide. In one embodiment, the thin protective layer 670 is deposited orgrown to a thickness in the range of approximately 50-300 Å, forexample, 50 Å. In one embodiment, the thin protective layer 670 can bean oxide grown by annealing a silicon substrate 600 in an oxygenambient.

The thin second spacer layer 640 is recessed by etching to form thespacer structure illustrated in FIG. 6l. In one embodiment, this etch isan anisotropic (directional) etch which will remove nitride, but notoxide. Examples of anisotropic etches are a dry etch or a plasma etch.

The thin protective layer 670 is removed and the thin first spacer layer630 recessed by etching a second time to form the spacer structureillustrated in FIG. 6m. In one embodiment, the thin first spacer layer630 is recessed approximately 60 nm deeper than the surface level of thegate layer 620. In one embodiment, this etch is an isotropic(multidirectional) etch which will remove oxide, but not nitride.Examples of isotropic etches are a wet, dry or chemical bath etch. Itshould be noted that the side walls of the gate layer 620 are nowexposed creating a larger contact (reaction) surface area.

In FIG. 6n, a reactant layer 680 is deposited, for example, by sputter,electron beam evaporation, chemical vapor, or plasma deposition. In oneembodiment, the reactant layer 680 can be a metal, such as titanium.

The reactant layer 680 and the gate layer 620 are then annealed to forma conductive layer 690 as shown in FIG. 6o. In one embodiment, theconductive layer 690 can be a polycide, such as titanium salicide. Apolycide may also be called a polysilicide. It should be noted thatsilicides can be self-aligning or non-self-aligning, and if the silicideis self-aligning, it may be called a salicide. It is to be understood byone of ordinary skill in the art that polycides, other thanself-aligning silicides, may also be formed. In one embodiment, theanneal may be performed using a rapid thermal annealing process in anitrogen ambient. In one embodiment, additional anneals can be performedto decrease the resistance of the conductive layer 690. It is to benoted that the conductive layer 690 can now extend beyond the edges ofthe gate layer 620 and is not constrained and stressed.

The unreacted reactant layer 680 is etched away leaving the conductivelayer 690 as illustrated in FIG. 6p. In one embodiment, this etch is anisotropic etch which will remove unreacted titanium, but not titaniumsalicide.

Through out the specification, reference has been made to isotropic andanisotropic etching. It should be noted that the present invention maybe performed using these etch processes interchangeably, however, suchinterchanging of etch processes may cause other complications. Theprocess steps as defined above are the preferred manner in which toperform the present invention.

Additionally, throughout the specification, it has been stated that theetch processes remove only the nitride or oxide layers, however, itshould be noted that such etch processes selectively remove the nitrideor oxide. In other words, an etch to remove nitride will remove nitrideat a faster rate than oxide, such that more nitride is removed and verylittle oxide is removed; and, an etch to remove oxide will remove oxideat a faster rate than nitride, such that more oxide is removed and verylittle nitride is removed.

The above described embodiments of the method and device of the presentinvention provide improved polycide resistance in polysilicon gatewidths below 0.20 μm. As earlier described, conductive layers, such asthe polycide, titanium salicide, can expand during formation. Previousgate electrode structures had spacer structures which constrained thisexpansion. This led to a stressed conductive layer that exhibitedincreased resistance. The several embodiments of the present invention,reduce the stress on the formed conductive layer thereby improving theresistance. In some embodiments, spacers are recessed to removeconstraints on the expansion of the conductive layer. In otherembodiments, spacers are partially recessed to provide thin spacer wallswhich flex to dissipate stress. In other embodiments, dual spacer stacksthat are recessed and partially recessed also provide dissipate orremove stress on the conductive layer. It is this reduction in thestress by the several embodiments of the present invention, thatprovides improved resistance. Also, in several of the embodiments theside walls of the gate layer are exposed to allow greater surface area.This aids in formation of the conductive layer by providing forincreased nucleation sites. By aiding in formation of the conductivelayer, process yields increase.

In the foregoing specification, the invention has been described withreference to specific exemplary embodiments thereof. It will, however,be evident that various modifications and changes may be made theretowithout departing from the broader spirit and scope of the invention asset forth in the appended claims. The specification and drawings are,accordingly, to be regarded in an illustrative rather than a restrictivesense.

What is claimed is:
 1. A method comprising: forming an insulative layerover a substrate; forming a gate layer over said insulative layer;forming a gate electrode by patterning said gate layer and saidinsulative layer; forming a thick first spacer layer over said gateelectrode and said substrate; forming a thick second spacer layer oversaid thick first spacer layer; removing said thick second spacer layerover top of said gate electrode and said substrate, leaving said thicksecond spacer layer adjacent to said thick first spacer layer to formthick second spacers, said thick second spacers having tops that areabout level with top of said gate electrode; removing said thick firstspacer layer over top of said gate electrode and said substrate byisotropic etching, leaving said thick first spacer layer adjacent tosaid gate electrode to form thick first spacers, said thick firstspacers having tops that are lower than top of said gate electrode;forming a reactant layer over said gate electrode, said thick firstspacers, said thick second spacers, and said substrate; forming aconductive layer where said reactant layer and said gate electrode arein contact, bottom of said conductive layer being approximately flat andabout level with tops of said thick first spacers; and removing anyunreacted reactant layer to leave an open space between said conductivelayer and said thick second spacers.
 2. The method of claim 1 whereinremoving said thick second spacer layer over top of said gate electrodeand said substrate to form thick second spacers is by anisotropicetching.
 3. The method of claim 2 wherein said insulative layercomprises oxide.
 4. The method of claim 3 wherein said gate layercomprises polysilicon.
 5. The method of claim 4 wherein said reactantlayer comprises metal.
 6. The method of claim 5 wherein said thick firstspacer layer comprises oxide formed to a thickness of approximately200-600 Angstroms.
 7. The method of claim 6 wherein said thick secondspacer layer comprises nitride formed to a thickness of approximately300-2000 Angstroms.
 8. The method of claim 7 wherein said conductivelayer comprises polycide that extends beyond edges of said gateelectrode and is not constrained and stressed by said thick firstspacers.
 9. The method of claim 8 wherein said reactant layer comprisestitanium.
 10. The method of claim 9 wherein said polycide comprisestitanium salicide (TiSi₂) which has a resistance that has been decreasedby additional anneals.